1) An acidulating substance 2) Food additive 
A substance added to food or beverages to lower pH and to impart a tart, acid taste. Phosphoric acid is an acidulant added to cola drinks.
<pharmacology> Food additive that is used to impart a sharp flavour. The most common acidulant is citric acid (produced by the fermentation of molasses or other sugars by the fungusAspergillus niger). Malic acid and fumaric acid are also frequently used. ... (06 May 1997) ... 
A food additive used to impart a tart, acidic taste to a food; may also assist in the setting of gels or to act as preservatives.
A substance added to food or beverages to lower pH and to impart a tart, acid taste. Phosphoric acid is an acidulant added to cola drinks. See also: Acid.
an acidulating substance.